Compiles the code in the file File, which is an
Erlang source code file without the .erl extension.
Options determine the behavior of the compiler.

Returns {ok,ModuleName} if successful, or error
if there are errors. An object code file is created if
the compilation succeeds with no errors. It is considered
to be an error if the module name in the source code is
not the same as the basename of the output file.

Here follows first all elements of Options that in
some way control the behavior of the compiler.

basic_validation

This option is fast way to test whether a module will
compile successfully (mainly useful for code generators
that want to verify the code they emit). No code will
generated. If warnings are enabled, warnings generated by
the erl_lint module (such as warnings for unused
variables and functions) will be returned too.
Use the strong_validation option to generate all
warnings that the compiler would generate.

strong_validation

Similar to the basic_validation option, no code
will be generated, but more compiler passes will be run
to ensure also warnings generated by the optimization
passes are generated (such as clauses that will not match
or expressions that are guaranteed to fail with an
exception at run-time).

binary

Causes the compiler to return the object code in a
binary instead of creating an object file. If successful,
the compiler returns {ok,ModuleName,Binary}.

bin_opt_info

The compiler will emit informational warnings about binary
matching optimizations (both successful and unsuccesful).
See the Efficiency Guide for further information.

compressed

The compiler will compress the generated object code,
which can be useful for embedded systems.

debug_info

Include debug information in the form of abstract code
(see
The Abstract Format
in ERTS User's Guide) in the compiled beam module. Tools
such as Debugger, Xref and Cover require the debug
information to be included.Warning: Source code can be reconstructed from
the debug information. Use encrypted debug information
(see below) to prevent this.
See
beam_lib(3)
for details.

{debug_info_key,KeyString}

{debug_info_key,{Mode,KeyString}}

Include debug information, but encrypt it, so that it
cannot be accessed without supplying the key. (To give
the debug_info option as well is allowed, but is
not necessary.) Using this option is a good way to always
have the debug information available during testing, yet
protect the source code.Mode is the type of crypto algorithm to be used
for encrypting the debug information. The default type --
and currently the only type -- is des3_cbc.
See
beam_lib(3)
for details.

encrypt_debug_info

Like the debug_info_key option above, except that
the key will be read from an .erlang.crypt file.
See
beam_lib(3)
for details.

'P'

Produces a listing of the parsed code after preprocessing
and parse transforms, in the file
<File>.P. No object file is produced.

'E'

Produces a listing of the code after all source code
transformations have been performed, in the file
<File>.E. No object file is produced.

'S'

Produces a listing of the assembler code in the file
<File>.S. No object file is produced.

report_errors/report_warnings

Causes errors/warnings to be printed as they occur.

report

This is a short form for both report_errors and
report_warnings.

return_errors

If this flag is set, then
{error,ErrorList,WarningList} is returned when
there are errors.

return_warnings

If this flag is set, then an extra field containing
WarningList is added to the tuples returned on
success.

return

This is a short form for both return_errors and
return_warnings.

verbose

Causes more verbose information from the compiler
describing what it is doing.

{outdir,Dir}

Sets a new directory for the object code. The current
directory is used for output, except when a directory
has been specified with this option.

export_all

Causes all functions in the module to be exported.

{i,Dir}

Add Dir to the list of directories to be searched
when including a file. When encountering an
-include or -include_dir directive,
the compiler searches for header files in the following
directories:

".", the current working directory of
the file server;

the base name of the compiled file;

the directories specified using the i option.
The directory specified last is searched first.

{d,Macro}

{d,Macro,Value}

Defines a macro Macro to have the value
Value. The default is true).

{parse_transform,Module}

Causes the parse transformation function
Module:parse_transform/2 to be applied to the
parsed code before the code is checked for errors.

asm

The input file is expected to be assembler code (default
file suffix ".S"). Note that the format of assembler files
is not documented, and may change between releases - this
option is primarily for internal debugging use.

no_strict_record_tests

This option is not recommended.
By default, the generated code for
the Record#record_tag.field operation verifies that
the tuple Record is of the correct size for
the record and that the first element is the tag
record_tag. Use this option to omit
the verification code.

no_error_module_mismatch

Normally the compiler verifies that the module name
given in the source code is the same as the base name
of the output file and refuses to generate an output file
if there is a mismatch. If you have a good reason (or
other reason) for having a module name unrelated to the
name of the output file, this option disables that verification
(there will not even be a warning if there is a mismatch).

If warnings are turned on (the report_warnings option
described above), the following options control what type of
warnings that will be generated.
With the exception of {warn_format,Verbosity} all
options below have two forms; one warn_xxx form to
turn on the warning and one nowarn_xxx form to turn off
the warning. In the description that follows, the form that
is used to change the default value is listed.

{warn_format, Verbosity}

Causes warnings to be emitted for malformed format
strings as arguments to io:format and similar
functions. Verbosity selects the amount of
warnings: 0 = no warnings; 1 = warnings for invalid
format strings and incorrect number of arguments; 2 =
warnings also when the validity could not be checked
(for example, when the format string argument is a
variable). The default verbosity is 1. Verbosity 0 can
also be selected by the option nowarn_format.

nowarn_bif_clash

By default, there will be a compilation error if a
module contains an exported function with the same name
as an auto-imported BIF (such as size/1) AND
there is a call to it without a qualifying module name.
The reason is that the BIF will be called, not
the function in the same module. The recommended way to
eliminate that warning is to use a call with a module
name - either erlang to call the BIF or
?MODULE to call the function in the same module.
The warning can also be turned off using this option,
but that is not recommended.The use of this option is strongly discouraged,
as code that uses it will probably break in a future
major release (R14 or R15).

{nowarn_bif_clash, FAs}

Turns off warnings as nowarn_bif_clash but only
for the mentioned local functions. FAs is a tuple
{Name,Arity} or a list of such tuples.The use of this option is strongly discouraged,
as code that uses it will probably break in a future
major release (R14 or R15).

warn_export_all

Causes a warning to be emitted if the export_all
option has also been given.

warn_export_vars

Causes warnings to be emitted for all implicitly
exported variables referred to after the primitives
where they were first defined. No warnings for exported
variables unless they are referred to in some pattern,
which is the default, can be selected by the option
nowarn_export_vars.

warn_shadow_vars

Causes warnings to be emitted for "fresh" variables
in functional objects or list comprehensions with the same
name as some already defined variable. The default is to
warn for such variables. No warnings for shadowed
variables can be selected by the option
nowarn_shadow_vars.

nowarn_unused_function

Turns off warnings for unused local functions.
By default (warn_unused_function), warnings are
emitted for all local functions that are not called
directly or indirectly by an exported function.
The compiler does not include unused local functions in
the generated beam file, but the warning is still useful
to keep the source code cleaner.

{nowarn_unused_function, FAs}

Turns off warnings for unused local functions as
nowarn_unused_function but only for the mentioned
local functions. FAs is a tuple {Name,Arity}
or a list of such tuples.

nowarn_deprecated_function

Turns off warnings for calls to deprecated functions. By
default (warn_deprecated_function), warnings are
emitted for every call to a function known by the compiler
to be deprecated. Note that the compiler does not know
about the -deprecated() attribute but uses an
assembled list of deprecated functions in Erlang/OTP. To
do a more general check the Xref tool can be used.
See also
xref(3)
and the function
xref:m/1 also
accessible through
the c:xm/1
function.

{nowarn_deprecated_function, MFAs}

Turns off warnings for calls to deprecated functions as
nowarn_deprecated_function but only for
the mentioned functions. MFAs is a tuple
{Module,Name,Arity} or a list of such tuples.

warn_obsolete_guard

Causes warnings to be emitted for calls to old type
testing BIFs such as pid/1 and list/1. See
the
Erlang Reference Manual
for a complete list of type testing BIFs and their old
equivalents. No warnings for calls to old type testing
BIFs, which is the default, can be selected by the option
nowarn_obsolete_guard.

warn_unused_import

Causes warnings to be emitted for unused imported
functions. No warnings for unused imported functions,
which is the default, can be selected by the option
nowarn_unused_import.

nowarn_unused_vars

By default, warnings are emitted for variables which
are not used, with the exception of variables beginning
with an underscore ("Prolog style warnings").
Use this option to turn off this kind of warnings.

nowarn_unused_record

Turns off warnings for unused record types. By
default (warn_unused_records), warnings are
emitted for unused locally defined record types.

Another class of warnings is generated by the compiler
during optimization and code generation. They warn about
patterns that will never match (such as a=b), guards
that will always evaluate to false, and expressions that will
always fail (such as atom+42).

Note that the compiler does not warn for expressions that it
does not attempt to optimize. For instance, the compiler tries
to evaluate 1/0, notices that it will cause an
exception and emits a warning. On the other hand,
the compiler is silent about the similar expression
X/0; because of the variable in it, the compiler does
not even try to evaluate and therefore it emits no warnings.

Currently, those warnings cannot be disabled (except by
disabling all warnings).

Warning

Obviously, the absence of warnings does not mean that
there are no remaining errors in the code.

Note that all the options except the include path
({i,Dir}) can also be given in the file with a
-compile([Option,...]). attribute.
The -compile() attribute is allowed after function
definitions.

Note also that the {nowarn_unused_function, FAs},
{nowarn_bif_clash, FAs}, and
{nowarn_deprecated_function, MFAs} options are only
recognized when given in files. They are not affected by
the warn_unused_function, warn_bif_clash, or
warn_deprecated_function options.

For debugging of the compiler, or for pure curiosity,
the intermediate code generated by each compiler pass can be
inspected.
A complete list of the options to produce list files can be
printed by typing compile:options() at the Erlang
shell prompt.
The options will be printed in order that the passes are
executed. If more than one listing option is used, the one
representing the earliest pass takes effect.

Unrecognized options are ignored.

Both WarningList and ErrorList have
the following format:

[{FileName,[ErrorInfo]}].

ErrorInfo is described below. The file name has been
included here as the compiler uses the Erlang pre-processor
epp, which allows the code to be included in other
files. For this reason, it is important to know to
which file an error or warning line number refers.

Analogous to file/1, but takes a list of forms (in
the Erlang abstract format representation) as first argument.
The option binary is implicit; i.e., no object code
file is produced. Options that would ordinarily produce a
listing file, such as 'E', will instead cause the internal
format for that compiler pass (an Erlang term; usually not a
binary) to be returned instead of a binary.

Determines whether the compiler would generate a beam
file with the given options. true means that a beam
file would be generated; false means that the compiler
would generate some listing file, return a binary, or merely
check the syntax of the source code.

Works exactly like
output_generated/1,
except that the environment variable ERL_COMPILER_OPTIONS
is not consulted.

Default compiler options

The (host operating system) environment variable
ERL_COMPILER_OPTIONS can be used to give default compiler
options. Its value must be a valid Erlang term. If the value is a
list, it will be used as is. If it is not a list, it will be put
into a list.

Inlining

The compiler can do function inlining within an Erlang
module. Inlining means that a call to a function is replaced with
the function body with the arguments replaced with the actual
values. The semantics are preserved, except if exceptions are
generated in the inlined code. Exceptions will be reported as
occurring in the function the body was inlined into. Also,
function_clause exceptions will be converted to similar
case_clause exceptions.

When a function is inlined, the original function will be
kept if it is exported (either by an explicit export or if the
export_all option was given) or if not all calls to the
function were inlined.

Inlining does not necessarily improve running time.
For instance, inlining may increase Beam stack usage which will
probably be detrimental to performance for recursive functions.

Inlining is never default; it must be explicitly enabled with a
compiler option or a -compile() attribute in the source
module.

To enable inlining, either use the inline option to
let the compiler decide which functions to inline or
{inline,[{Name,Arity},...]} to have the compiler inline
all calls to the given functions. If the option is given inside
a compile directive in an Erlang module, {Name,Arity}
may be written as Name/Arity.

Example of explicit inlining:

-compile({inline,[pi/0]}).
pi() -> 3.1416.

Example of implicit inlining:

-compile(inline).

The {inline_size,Size} option controls how large functions
that are allowed to be inlined. Default is 24, which will
keep the size of the inlined code roughly the same as
the un-inlined version (only relatively small functions will be
inlined).